The invention relates to an enossal implant for the fastening of a firmly seated denture in the mouth. The enossal implant includes a post, one end of which serves for the fastening of the firmly seated denture and the other end of which is connected with an anchoring surgically introducible into a jaw bone.
The invention relates, furthermore, to devices for the exact-fit reaming of a slit in a jaw bone and for the exact-fit reaming of a cylindrical hole in the region of the slit in a jaw bone as well as to a setting instrument for driving the enossal implant into the reamings of the jaw bone.
It is known to have an enossal implant for the fastening of firmly seated denture or tooth replacement. This prior implant has a post that is essentially rectangular in its cross section, that tapers upwardly, and that is securely emplaceable on a denture provided with a corresponding recess. The post extends downward into a thin neck and then widens, laterally, into a flat, narrow band, from which sharp lashings extend downward. The lashings widen into a swallowtail form, in the plane of the narrow lug, and are made wedge-shaped in its cross section, as well as with depressions for the snug-form embedding in the jaw bone. Underlying this known implant is the thought of using as extensive and sharp a branching as possible of the part of the implant embedded in the jaw bone, in order thereby to achieve a good anchoring or embedding of the implant in the jaw bone. A disadvantage of this known implant lies in that the strip-form part embedded in the jaw bone, from which the lashings extend, is relatively flexible, so that on burdening of the denture, the forces transferred over the neck of the implant to the strip-form part lead to bending of the strip-form part which can result in relative movement of the strip in the jaw bone. Thus there exists the danger of a traumatization of the parts of the jaw bone bordering on the implant. This danger is especially great for the reason that from the strip-form part, the lashes extend away and the ends of the lashes, by reason of the geometrical relations or shapes, move laterally to an increased degree in case of the bending of the strip-form part.
Finally, an appreciable disadvantage with respect to this prior implant lies in that the lashings, extending from the strip-form part into the jaw bone, converge in wedge-form, in the vertical section, and, therefore, form no flat support surfaces by reason of the forces arising in chewing pressure. The wedge-form of the lashings brings about rather, in correspondence to the parallelogram of forces, a pressure increase and thereby an additional loading of the bone tissue. In other words, the wedge-shaped lashings, in the case of chewing pressure, press themselves into the bone tissue in the manner of a wedge.
Underlying the present invention is the problem of providing a firmly-seated denture, in which the disadvantages of the known implant do not occur, in which relative movements of parts of the implant, with respect to one another in the zone of the jaw bone, are reduced to a minimum and in which no high specific surface loads have to be absorbed by the jaw bone tissue. The implant of the present invention, furthermore, is to be easily producible and accurately and securely introducible into the jaw bone. Moreover, there is to be provided the possibility of driving the implant of the present invention accurately and securely into corresponding reamings-out of the jaw bone.
The problem underlying the present invention is solved by novel means wherein the anchoring or embedding means of the implant consists of a cylindrical part running essentially in extension of the post, from which part there extends laterally at least one carrying arm which has, transversely to the axis of the cylindrical part, a slight expansion and in the direction of the axis, a larger expansion.
The cylindrical part of the implant, according to the present invention, provides for a rigid transfer of the burdening forces from the denture to deep into the jaw bone. This rigid part makes possible the fastening of the carrying arms, rigid in respect to the chewing forces. Their rigidity is assured by the great expansion of the part, in direction parallel to the axis of the cylindrical part, so that the forces are transferred from the cylindrical part onto the rigid carrying arms and from these arms to the bone tissue, without there occurring appreciable relative movement between any parts of the implant and the jaw bone. In other words, the use of the improved implant excludes an uneven distribution of forces on the bone tissue in the jaw bone because of the unlikelihood that relative movement between implant and bone tissue will occur when chewing movements occur.
A further advantage of the present invention consists in that the cylindrical part has a threaded bore for releasable fastening of the post which is provided with a threaded pin. This bore can serve for a fastening of the denture, fastened releasably by the doctor but seated firmly for the patient. It can, however, simultaneously serve for the centering of a setting instrument in the setting of the implant in a corresponding reaming-out of the jaw bone.
A still further advantage of the present invention lies in that the narrow edges of the carrying arm of the implant are constructed continuously, without interruptions and in such a manner that the material of the carrying arm, in the zone of the narrow edges, define a carrier having continuous upper and lower trusses. This construction of the carrying arm provides maximum rigidity or stiffness in the carrying arms thereby avoiding the danger of local increases in the specific surface load.
To increase the supporting or engagement surfaces of the carrying arms, on the bone tissue, without giving up the utility of continuous upper and lower trusses of the carrying arms, it is expedient that the carrying arm have recesses in the zone between the border zones of the narrow edges. These recesses can have the form of lengthwise slits whose longest extent is essentially perpendicular to the axis through the cylindrical part. They can also have the form of slits that run substantially parallel to the axis of the cylindrical part. The course of the slits depends on the possible expansion or extension of the carrying arms in a direction parallel to the axis of the cylindrical part. In general, this extension should be as great as possible. It is limited by the vertical extension of the jaw bone and by medical circumstances as well as by the location of the implant in the jaw bone along the rows of teeth.
Another further advantage of the present invention consists in that the cylindrical part has on its end, away from the post, preferably spherical roundings. It is expedient, too, that the narrow edges of the carrying arm or arms and the recesses or slits be rounded. All these roundings bring about, in contrast to the deliberately sharply formed edges of the known implant, as uniform as possible a loading of the bone tissue. Furthermore, it is expedient that the cylindrical part go over into the carrying arms with roundings.
A further advantage of the present invention consists in that the upper edge, facing the post, of the carry arm or arms, runs remote from the upper edge of the cylindrical part facing the post. Thus the cylindrical part projects somewhat beyond the upper edge of the carrying arms so that it can serve for the lateral engagement of a driving-in instrument so that the position of the driving instrument can be fixed relative to the carrying arms.
The improved implant according to the present invention can be introduced especially well into reamings-out of the jaw bone with the aid of a setting instrument. This setting instrument is characterized by a plate from which there projects perpendicularly at least one lug that has a supporting shoulder whose extent, in a direction parallel to the plate, corresponds essentially to the extent of the carrying arm. The plate forms a good attack surface for driving-in instruments, for example, a hammer or the like. Simultaneously the plate makes possible the determination of the penetration depth and the exact position of the implant.
A further advantage of the setting instrument of the present invention consists in that the distance of the support shoulder from the surface of the plate corresponds to the driving-in depth of the implant into the jaw bone. By choice of setting instruments, with differing distance between support shoulder and plate, it is possible to predetermine the driving-in depth of the implant. In the driving-in process, the plate comes into engagement on the upper edge of the jaw bone and thus prevents an undesirably deep or uneven driving in of the implant.
A still further advantage of the setting instrument of the present invention consists in that the plate has a fitting pin means extending in the direction of the lug or lugs, which is conducted through a corresponding recess in the cylindrical part. The fitting pin means has a pin having threads screwable into a central threaded bore of the cylindrical part and engageable slidably into a, fitting bore in the plate. The fitting pin means holds the setting instrument laterally in an exactly fixed position, with respect to the implant, so that damage to the jaw bone is avoided.
The slit in the jaw bone for the implant, according to the present invention, can be made especially accurately by means of an oblong template. The template includes a guide slot corresponding to the length of the slit to be made and has at least one fitting pin for insertion into a fitting hole. The slot is made by means of a reamer which can be installed in a hand piece and which has a cylindrical fitting surface whose diameter corresponds to the width of the guide slot. By the use of such a template, the course of the slit in the jaw bone is firmly prescribed. The position of the template with respect to the jaw bone is determined by a fitting pin, which engages in a corresponding fitting hole. This fitting hole can have a form which corresponds exactly to that of a pin of an implant for fastening a firmly seated denture. Thus no holes or recesses are made in the zone of the jaw bone that are not used later. The cylindrical fitting surface of the reamer is guided exactly by the guide slot so that tiltings are largely avoided.
A further advantage of the present invention consists in that the template has, along the guide slot, a stop surface against which, with reamer fully introduced, an axial stop surface provided on the reamer abuts and thus this structure determines the depth of the slit to be reamed. Through this further advantage, the depth of the slit in the jaw bone is exactly determined by the distance between the front end of the reaming part of the reamer and the axial stop surface. According to this further advantage of the present invention, reamers may be used in which, between the reaming part of the reamer and the axial stop surface, there is arranged a cylindrical shaft whose diameter corresponds to the diameter of the reaming part. Use of several reamers which have cylindrical shafts of varying lengths permits the slit to be slowly enlarged in depth. In this regard, the cylindrical shaft comes into engagement, between the reaming part of the reamer and the axial stop surface, with the walls of the already reamed slit part so that as the depth of the slit increases, the guidance takes place increasingly but not solely by reason of the template, but also by reason of its engagement on the reamed slit. This assures an especially high accuracy of reaming or milling of the slit.
It is expedient that the reaming part of the reamer tapers conically toward the end. As a result of this structure, the reaming part of the reamer is guided with its circumference in the slit being reamed by it. In contrast with a cylindrical construction and because of turning inaccuracies and vibrations, the reamed slit would always be greater than the cylindrical reaming or milling part so that there would be achieved neither an engagement on the rearward cylindrical milling part nor an engagement on the cylindrical shaft.
A still further advantage of this present invention consists in that the fitting pin lies in the zone of the guide slot. The fitting pin has a diameter that is greater than the width of the guide slot, such that the guide slot extends through the fitting pin. With the use of such a fitting pin there is assured the greatest security against turning of the template despite use of only one fitting pin. This is particularly important in, for example, the case of the reaming of a slit into a jaw bone laterally from the gum, wherein the template is aligned through engagement from outside, and especially through engagement on the cut edges of the gum in the zone of the slit to be reamed.
A further advantage of the present invention consists in that a fitting sword is provided whose cross section substantially corresponds to the cross section of the reaming part. The fitting sword is insertable in the guide slots and in the partially reamed slit in such a manner that the template is secured against twistings, the fitting sword filling only a part, preferably less than half, of the guide slot. This fitting sword assures an even better security against twisting. As noted above, the fitting sword fills only a part of the guide slit and of the reamed slit so that in each case, the other part of the slit is free for reaming. When this other part of the slit is reamed or reamed deeper, then the fitting sword can be inserted in this other part so that the reaming can then take place in the part at which previously that fitting sword was inserted.
The present invention relates, furthermore, to a template for the production of a cylindrical hole in the zone of the slit. This template is characterized by a base plate from which there extends on one side, two swords whose cross sections correspond essentially to the width of the reamed slit. Thus, by inserting the swords in the reamed slit, the base plate is fixed on both sides of the cylindrical hole to be made. In the base plate, there is also a cylindrical guide hole for the accurate guidance of a cylindrical finished shaft of a reamer. With this template it is possible, for example, to ream out a hole in the region of the guide slit. The same process used for reaming the slit can be utilized for reaming the fitting hole, namely, introducing fitting parts into parts of the reaming recesses in order then to carry out the reaming operations in the zone not occupied by these fitting parts. As with the template used for the slit, the template for the hole is provided with guide surfaces for the guidance of the reamer which has corresponding cylindrical fitting surfaces. The base plate can, to be sure, depending on the purpose of use, have a different thickness, in order to give the cylindrical guide hole a sufficient guide surface. The base plate can, however, also be arranged so that a fitting sleeve extends on the side away from the fitting swords. The inside wall of this sleeve forms an extension of the guide hole in the base plate and this assures an especially good guidance between reamer and template.
In order to assure a satisfactory guidance over the entire reaming depth, especially even when the reamer is near the reaming depth, it is expedient that the length of the fitting shaft be greater than the depth of the cylindrical hole to be made. It is also expedient that at the root of the fitting shaft, there is an axial stop surface which abuts against a corresponding stop surface on the base plate or the fitting sleeve. This arrangement can thus determine the depth of the cylindrical hole to be made. Moreover, it is expedient that the diameter of the cylindrical fitting shaft of the reamer be greater than the greatest diameter of the reaming, milling head. As a result of this construction, the reaming head can be put through the guide hole of the template without any damage being done to the guide surfaces of the guide hole. An introduction of the reamer with the template installed is also possible.
A still further advantage of the template of the present invention consists in that between the reaming head of the reamer and the fitting shaft, there is a stem zone whose diameter is smaller than the diameter of the reaming head. Through the free space formed in the zone of the stem, the leading off of the reamed material is permitting such that taking the reamer out of the guide hole the material can escape. It is also expedient, however, for the cylindrical fitting shaft to be provided with grooves or holes through which, for example, rinsing fluids can be introduced and the rinsing agent led off, together with the cleared out or reamed out reaming material.